1. Field Of The Invention
This invention relates to processes for applying an autodepositing composition in the form of a resinous coating on metallic surfaces. More specifically, this invention relates to processes of applying an autodepositing composition by a flowing stream or spray of the composition onto metallic surfaces.
2. Discussion of Related Art
Autodeposition is a process whereby an aqueous resinous coating composition of low solids concentration (usually less than about 10% by weight) forms a coating of high solids concentration (usually greater than about 10% by weight) on a metallic surface. The surface is immersed in an autodeposition bath with the coating increasing in thickness and/or weight the longer the time the metallic surface is immersed in the composition.
Autodeposition is similar to electrodeposition, but does not require the aid of external electrical current to cause the resin particles to deposit on the metal surface. In general, autodepositing compositions are aqueous acid solutions having solid resin particles dispersed therein.
The autodeposition process is typically carried out in the following manner. The metallic surface is precleaned and rinsed with water. The precleaned surface is then immersed in the autodepositing composition for a period of time within the range of about 30 seconds or less to about 3 minutes. The composition is typically agitated during the autodeposition process and may be heated if heavier coatings are desired.
The process of autodeposition by immersing the metallic surface in the autodeposition bath, while commercially viable, is less than desirable for coating objects where only a portion of the surface is to be coated, such as in the production of shock absorbers. Those surfaces which are not to be coated must be masked during autodeposition and the mask removed after the object has emerged from the bath. This procedure is time consuming and adds significantly to the cost of the autodeposition process.
It would, therefore, be desirable to provide a method of applying an autodeposition coating to a metallic surface, or portion thereof, without immersing the object to be coated in a bath.